Why can't people figure out warp versus runout versus disc thickness variation

To be sure of their meaning, you will need to be fluent in Korean and read the original paper in its native language, Korean.

I'm not sure the paper is actually written originally in Korean, are you?

The authors seem completely ignorant that the word "warp" has two different meanings, one of which is the colloquial abuse of the word, while the other is the technical use of the word.

Given that it's a technical paper, I'm astounded that they used the colloquial term, and even more so astounded that we can assume that's a peer reviewed paper, where one wonders how it got accepted given the horrid abuse of the English language.

Given the paper equated "warp" with DTV & lateral runout, this description is apropos to describe what those two latter terms mean, technically speaking: Stop the ??Warped?? Rotors Myth and Service Brakes the Right Way Where that author advises: "Starting today, remove ??warped rotor?? from your vocabulary. Instead, you should be both looking for and educating your customers about these terms: Lateral Runout & Disc Thickness Variation (DTV)"

Odds are the authors are not fluent in English and they had a grad student translate for them. There is no telling what they orginally meant.

"The Effect of Residual Stress on the Distortion of Gray Iron Brake Disks"

Authors Authors and affiliations

M. W. Shin G. H. Jang J. K. Kim H. Y. Kim Ho JangEmail author

M. W. Shin 1 G. H. Jang 1 J. K. Kim 2 H. Y. Kim 2 Ho Jang 1 Email author

Are you assuming that the 'or' means they are equating 'warping' with 'thickness variations'? Maybe they just mean that either condition can cause pulsations.

Again, maybe they mean that 'dimensional instability' can modify either runout or DTV, causing brake judder, without equating the two distiortions.

{trimmed}.

I fully agree that the "or" is confusing in and of itself, but I read the entire paper, so I know what they *measured*, where they did NOT measure warp.

Warp is easily measured since anyone who checks a head, for example, measures it for warp. You use a known-straight surface and then you use feeler gauges to see the variation in "flatness" to that known flat surface.

From the word "or", I agree with you the authors' intent is ambiguous - but from their measurements, they clearly measured DTV and lateral runout.

I think they intended on proving that *heat treating* caused less lateral runout and/or less disc thickness variation - which I'm sure they did accomplish.

But that's not the same thing as warp, which is not only the word they used repeatedly, but which was the reason that the person referred me to that paper, since *he* thought the paper had something to do with warp.

It didn't. It just used the word. But they abused the English language in using the word (IMHO).

That boggles the mind that people are _that_ sloppy using that technical term, particularly because disc rotors can't warp (as in potato chip) because the temperatures required are impossible to achieve according to the reliable references I've seen.

Raybestos says: "Brake rotors do not warp from heat..."

This says: "Rotors are cast in extreme heat three to five times greater than the most aggressive braking situation. Physically, warping a rotor would require a similar application of extreme heat, which is impossible."

This says: "...the temperature required to make metal that resilient soft enough to simply bend would be tremendous."

This says that there are adverse effects starting at 1200dF: "When this local temperature reaches around 1200 or 1300 degrees F. the cast iron under the deposit begins to transform into cementite (an iron carbide in which three atoms of iron combine with one atom of carbon). Cementite is very hard, very abrasive and is a poor heat sink. If severe use continues the system will enter a self-defeating spiral - the amount and depth of the cementite increases with increasing temperature and so does the brake roughness."

This says: "in more than 40 years of professional racing, including the Shelby/Ford GT 40s, one of the most intense brake development program in history - I have never seen a warped brake disc."

These say the myth of warped rotors started in the 1970's:

This non-scientific thread, which we can quickly assume isn't scientific so let's just take it as a reasonable point of view only, says that the surface may get to 600dF but the rest of the rotor is at a lower temperature than the surface.

It's pretty clear from this (and other references) that the authors abused the term "warp" - but since the long term solution for a warped rotor is completely different than the long term solution for a rotor with lateral runout or disc thickness variation, it's *important* the distinction.

NOTE: A compounding factor is that the short-term solution to warp is the

Hence, use of the wrong terminology has many dollars of unintended consequences (likely hundreds of millions of wasted money every year, IMHO).

Bad translations by non-native speakers will always be with us. When you're using a language that's not your own, it's not always easy to find le mot juste.

Using the wrong technical term in a technical paper is a problem, of course, but it hardly amounts to an abuse of the English language.

Now, if the disk had capsized, ...

I bought a 97 Contour in 2001, and it had brake pulsation. I called it warped rotor, not caring much what was the precise distortion that caused the pulsation. I replaced all four rotors myself for $105. Not really big money. It's been a long-term solution: I still keep the car for pulling a trailer, and the problem has never returned. Maybe they weren't 'warped', or maybe they were, by careless lug nut tightening.

Another sort of physics/language problem -

"Rotors are cast in extreme heat three to five times greater than the most aggressive braking situation."

I don't think it makes sense to speak of multiples of temperature unless you are referencing to absolute zero.

Agreed that the abuse of the word "warp" has zero negative effects ... if ... if ... if ... if ... if .... if ... if ... if ... if...

Remember the Spartan's response to the "if we attack you" diplomatic 'cable' way back in the days of the Greeks? The keyword is if.

If you actually *act* on "warp", you'll do the most insane things, and, in the end, you'll *still* have your vibration.

Thats' because the long-term solution for warp is *different* than the long term solution for, say, lateral runout or disc thickness variation.

The short term solution is the same - but the long term solution is completely different.

That's the main reason it matters.

It doesn't matter what you call it. The fix is still the same. My guess is that the warping problem is caused by hard braking and the resulting transf er of friction material from the pads to the rotor surface. This occurs on a molecular level and results in the rotor surface acquiring areas of diffe ring friction coefficients. This can cause hot spots on the rotor when brak ing. To that effect, I try not to clamp down too hard on the brakes after c oming to a stop when going down a hill. That's pretty the only thing that c an be done to protect your rotors.

I acted on "warp", sensibly replaced my rotors, and it solved the problem permanently.

Two things commonly happen:

1. Something goes wrong with your suspension causing a slight shimmy. Maybe a ball joint is loose, maybe a rod is bent. As you brake, the shimmy causes the pressure on the rotor to change and soon a "warp" is worn into the rotor surface.

1. Someone tensions your lug nuts without using a torque wrench. Maybe they use torque sticks and are sloppy, maybe they do it by hand with a maltese cross and a hammer. Uneven pressure is placed on the rotor, and the same uneven wear pattern results. If you're really lucky, your lugs break off too.

Avoiding these two situations will cause your brake rotors to last much longer.

--scott

Well, that sounds reasonable.